There exist many processes in the energy industry, the refining industry or the petrochemical industry during which a mixture of nitrogen and hydrocarbon(s) is formed. For example, during the production of polypropylene from propylene, nitrogen is used to purify the polymer and in particular in order to entrain the propylene which has not reacted during the polymerization. In general, the propylene also comprises a small fraction of propane.
The mixture of nitrogen and hydrocarbons often cannot be recycled in the process. The mixture is thus incinerated and discharged to the air.
It would thus be desirable to be able to recover in value this mixture of nitrogen and hydrocarbon(s). In particular, it would be desirable to be able to separate the nitrogen from the hydrocarbon(s) and to recover high-purity nitrogen using a system which consumes the least possible energy and which has the highest possible yield. It would also be desirable to be able to recover the hydrocarbons with a high purity and a high yield.
It is possible, for example, to use condensation or membrane techniques or a combination of the two to recover the hydrocarbons. However, the method is expensive and yields are generally low.
The separation techniques also comprise absorption by a chemical solvent (for example amines) or distillation. However, these processes require bulky installations with high operating expenses (OPEX) and capital expenses (CAPEX).
Another solution consists in using solid adsorbents subjected to adsorption and desorption cycles. The desorption stage can be carried out either while reducing the pressure by pressure swing adsorption (PSA) or else while increasing the temperature by temperature swing adsorption (TSA).
Conventional solid adsorbents comprise active charcoal, activated aluminas, silica gels or else other porous metal oxides. However, the adsorption capacity of these adsorbents is insufficient to compete with the industrial processes described above.